The frictional resistance of a vessel hull as it moves through the water can constitute 45% to 90% of the total resistance and may be increased by 6% up to 80% due to the fouling of the hull by algae, sea grass, barnacles, and the like. An added resistance of 30% due to moderate bio-fouling of a tanker hull can increase the fuel consumption of the vessel by twelve tons per day. The result is added cost to operate the vessel and increased emissions.
Accordingly, there are a variety of methods employed to lower the chance of bio-fouling and/or to clean the hull of vessels. For example, hull paints and coatings are used in an effort to decrease the chance of bio-fouling, but such treatments do not always work reliably. See, for example, U.S. Pat. No. 7,390,560. Also, the vessel must be dry docked for an extensive period of time while the paint and/or coating is applied. There are also environmental concerns with anti-fouling paints and coatings.
Most prior hull cleaning robots suffer from several potential shortcomings. Typically, the robots are connected to a cable and powered and controlled by an on-board power supply and control subsystem and are able to operate only on a stationary vessel.